Study of a circuit-breaker arc with self-generated flow. III. Thepost-arc phase

For pt.II see ibid., vol.16, p.615-22, 1988. The third part of this study of a circuit-breaker arc with self-generated flow concerns the model of the post-arc phase. The greater interruption capability of SF₆ compared to N₂, already suggested in pt.II, is confirmed by the following results: amplitude and duration of the postarc current are much lower in SF₆ and the maximum value of the rate of rise of recovery voltage is about three times higher in SF₆ than in N₂. The model also predicts the existence of a plateau in post-arc current variation and the original behavior of this type of circuit-breaker: interrupting efficiency increases with the current peak in the initial phase     

小型场畸变气体开关的击穿抖动特性

基于高功率重复频率脉冲功率源的应用需求,研制了一种三电极场畸变结构气体火花间隙开关,并开展了重复频率条件下的触发特性研究。实验研究了场畸变火花间隙开关的触发特性随重复频率、气体成分、工作压强和工作系数的变化关系,计算了气体开关的触发击穿时延和抖动参数,分析了影响开关触发特性的主要因素。实验结果表明:气体开关触发击穿的抖动随着重复频率增加而增大;填充气体中SF₆和N₂体积比1∶1时,混合气体的综合性能较好;工作系数主要影响开关第二放电火花间隙(间隙2)的击穿抖动。     

Excitation, ionization, and reaction mechanism of a reactivecathodic arc deposition of TiN

This paper discusses the excitation, ionization and reaction mechanism of reactive cathodic arc deposition of TiN. Such arc plasmas art operated in the arc discharge type PVD apparatus. The 50 A arc is operated in N₂ atmosphere of 0.13 to 26.6 Pa. The arc voltage, the electron energy distribution and the spectral intensities are measured as a function of pressure. The deposited films are analyzed by XPS. It follows from the result that (1) the N₂ molecules impact with the high energy electron to be excited or ionized; (2) Ti ⁺⁺ ions which are initially emitted from the cathode spot recombine with electrons and turn Ti⁺ ions and Ti atoms and the recombination ratio increases with increasing pressure; (3) the TiN compound is produced on the substrate surface in the ensuing process, the excited N₂ are adsorbed on the substrate surface, the N ₂ are dissociated to N atoms through collisions with Ti⁺ ions of 40-60 eV, the N atoms react with the Ti atoms to form TiN     

Studies and performance of decreased rail gap switch inductance byenhancing multichanneling via gas mixture

In pulsed power technology, a pressurized gap switch has been mainly utilized to produce a high power pulse. A multichannel rail gap switch has been widely utilized not only to obtain extremely low inductance, low resistance switching but also to reduce the damage of the electrode. A self-elected multichannel rail gap switch was developed. The switch was operated with pure SF₆ and the mixture of SF₆ with N₂, channel numbers of 20 and 100 were obtained with low switching inductance's of 15 nH and 9 nH, respectively     

The influence of an electronegative gas admixture on the intenseE-beam transport and induced plasma currents in argon

The propagation of an electron beam, with electron energy ~1.2 MeV, beam current ~8 kA, and an induced plasma current is investigated using a metal drift tube ~0.5 m long filled with argon at atmospheric pressure. The behavior of electron concentration and electron temperature was calculated for several concentrations of the SF₆ admixture. The comparison of the results of the experiments and numerical calculations shows that the dropping of plasma current when electronegative gas is added is due to the electron attachment to the SF ₆ molecules. The results of the experiment and the calculations provide the evidence of at least three mechanisms responsible for the increase of the REB transport efficiency when electronegative gas is present     

基于飞秒激光引导高压放电的SF6分解物原位检测

气体绝缘开关设备(GIS)绝缘缺陷引发的放电会导致SF₆分解,分解产生的低氟硫化物与设备内的微量H₂O和O₂反应生成具有腐蚀性的物质,影响设备正常运行,因此,研究SF₆分解机理对GIS的安全运行具有重要意义。由于部分分解物在采样过程中发生转化,因此,实现SF₆分解物的原位检测对于研究SF₆分解机理是十分必要的。采用飞秒激光引导高压放电实现了高压放电空间和时间的精确控制,并利用飞秒激光引导高压放电产生的空间分辨光谱实现了SF₆分解物的原位测量。首先研究证明了飞秒激光不会引起SF₆的分解;其次,利用飞秒激光产生的等离子体通道实现了放电空间和时间的精确控制;最后,发现分解物中包含由于高能电子碰撞直接或间接产生的大量S和F的离子和原子。研究证明了基于飞秒激光引导高压放电可以实现SF₆分解物的原位检测,为开展高压放电下SF₆分解机理研究提供了一种新的研究手段。     

High adsorption and separation performance ofCO2 over N2 in azo-based (N=N) pillar[6]arene supramolecular organic frameworks

Azo-based pillar[6]arene supramolecular organic frameworks are reported for CO₂ and N₂ adsorption and separation by density functional theory and grand canonical Monte-Carlo simulation. Azo-based pillar[6]arene provides suitable environment for CO₂ adsorption and selectivity. The adsorption and selectivity results show that introducing azo groups can effectively improve CO₂ adsorption and selectivity over N₂, and both CO₂ adsorption and CO₂ selectivity over N₂ follow the sequence pillar[6]arene_N4 > pillar[6]arene_N2 > pillar[6]arene. Pillar[6]arene_N4 exhibits CO₂ adsorption capacity of ～ 1.36 mmol/g, and superior selectivity of CO₂ over N₂ of ～ 116.75 with equal molar fraction at 1 bar (1 bar=10⁵ Pa) and 298 K. Interaction analysis confirms that both the Coulomb and van der Waals interactions between CO₂ with pillar[6]arene frameworks are greater than that of N₂. The stronger affinity of CO₂ with pillar[6]arene_N4 than other structures and the larger isosteric heat differences between CO₂ and N₂ rendered pillar[6]arene_N4 to present the high CO₂ adsorption capacity and high CO₂ selectivity over N₂. Our results highlight the potential of azo-functionalization as an excellent means to improve pillar[6]arene for CO₂ capture and separation.     

大功率电弧加热器起弧过程流场特性研究

电弧等离子体是通过电极之间击穿放电,产生热电弧,实现对冷态介质加热,目前大功率的电弧等离子体发生器在航空航天领域有重要的应用,是国内外开展飞行器防热材料筛选和考核研究最重要的地面模拟试验设备.本研究基于发展的高焓气流非接触式光谱诊断方法,开展对10 MW量级大功率长分段电弧加热器起弧过程流场特性的定量、定性研究,在线测...     

Mechanisms of metastable N2 and Kr electron stimulated desorption from N2---Kr double layer and mixed films

Desorption of metastable particles from layered and mixed films, composed of N₂ and Kr, is induced by the impact of 6–50 eV monoenergetic electrons. From yield functions and time-of-flight analysis of the metastable particles emanating from these films, N*₂ and Kr* are identified as the desorbing species. Basic mechanisms responsible for their desorption are discussed. It is suggested that the desorption of Kr* arises from dissociation of transitory [Kr·N₂]* excimers. The desorption of N*₂ can arise from cavity expulsion, intramolecular vibrational energy transfer (with or without prior electronic excitation energy transfer from Kr excitions to N₂) and the dissociation of [Kr·N₂]* excimers.     

Study of a circuit-breaker arc with self-generated flow. II. Theflow phase

For pt.I see ibid., vol.16, no.6, p.606-14 (1988). The experimental results presented concern the variations of the mean electric field and gas mass flow during this phase. The most important part consists of a modeling of the evolution of the interruption arc during the decrease of the current from 1000 A to 0. In this modeling, based on the conservation equations of mass and energy, the boundary conditions are determined by an approximate separate modeling of the arc whereas turbulence is treated through Prandtl's approximation. This theoretical study has been developed in the case of SF₆ and nitrogen. The computed values of the electric field and temperature show that the arc has a quasi-stationary behaviour as long as the current intensity is greater than a few tens of amperes, for a decay rate of 1.35 A/μs. The energy losses are governed by radiation at high current and by turbulence conduction at low current. The most important results concern the conductance, whose evolution time constant, immediately prior to current zero, is 3.5 μs in SF₆ and 15 μs in nitrogen. The difference is essentially due to variations with temperature of thermal conductivity and specific heat in two gases     

Pressure limits for the vacuum arc deposition technique

Observations of the cathodic copper plasma expansion at low pressures of He, Ar, and SF₆ showed that, for background gas mass densities of ρ_g=1 to 4×10^-4 kg/m ³ and higher, the plasma and gas are separated into two volumes. A shock wave acts as a boundary between the two volumes. The boundary attains a stationary position once its expansion velocity decreases to the velocity of sound in the background gas. This position corresponds to a distance R_c to the cathode that agrees with a snowplow expansion model, giving R_c ^βf=E_r, where f is a function of the arc current and background gas characteristics, E _r is the erosion rate of the cathode, and β varies between 2.1 and 2.5. The interaction model is based on kinetic energy exchanges between two gas-like volumes without other energy losses. A maximum pressure limit for vacuum arc deposition is set for ρ_g /I=2 to 9×10^-6 kg/m³ A     

Electric power switches

A review is given of the physics and engineering behavior of arcs in vacuum and axial gas blast under the conditions found in high-voltage circuit breakers. The topics included are: the zero energy switch; current limiting switches; arc control; the gas-blast circuit breakers; the low-current gas-blast arc; arcing with ablation; interruption dynamics; arc modeling; vacuum as a switching element; the vacuum arc; the constricted arc; and the properties of SF₆     

Investigation of arc roots of constricted high current vacuum arcs

The anodic and cathodic arc roots of constricted high current vacuum arcs were investigated with a fast framing charge-coupled device camera of 1 μs exposure time. The experiments were performed with cup-shaped contacts, with sinusoidal currents of amplitudes between 20 and 100 kA, and a sine halfwave duration of 10-12 ms. The arcs were drawn by contact separation and accelerated by the Lorentz force between the arc current and the transverse magnetic field generated by the contrate contact. The anode and cathode arc roots behave reproducibility and arc scaleable within the range of currents investigated. Both types of arc roots are elliptical, with a major to minor axis ratio of 1.4. The major axis points are in the direction of arc propagation. Anodic and cathodic arc root cross-sectional areas as a function of current can both be described by a potential law with a common exponent of 0.76. For currents of 20-100 kA, mean current densities of 81-121 and 41-60 kA/cm ² were found in anode and cathode arc roots, respectively. Estimations of their temperature and vapor densities were performed. For the investigated current range T_A≈3300-3600 K, n_A ≈1.6*10¹⁹-2.2*10¹⁹cm^-3 and T _C≈3200-3400 K, n_C≈0.8*10¹⁹-1.2*10 ¹⁹ cm^-3 were found for anode and cathode, respectively     

Pressure dependence of plasma parameters in medium-vacuum nitrogenarc discharge with the titanium cathode

The plasma properties of a medium-vacuum nitrogen arc discharge from a titanium cathode were studied. The arc chamber use was 400 mm in diameter and 600 mm in length. The cathode diameter and thickness were 64 and 25 mm, respectively. The experimental conditions are given as follows: pressure range=1×10^-3~2×10^-1 torr; N₂ gas flow rate=6 ml/min; arc current=50 A. Electric probe characteristics are measured as a function of pressure and distance from the cathode surface. The analytical results obtained show that the electron energy distribution takes 1-Mx at pressures above 1×10^-2 torr but 2-Mx at pressures under 4×10^-2 torr and that the electron density has a maximum value at a certain pressure. The Ti⁺, Ti⁺⁺, and N ⁺₂ ion spectral intensities are measured as a function of pressure and distance from the cathode surface. On comparison of these results and the electron density, the Ti⁺ spectral intensity turns out to be proportional to that of the electron density. This suggests that the major ion in the plasma volume is of the Ti⁺ species     

Excitation and relative differential oscillator strengths for trifluoromethyl sulphur pentafluoride, SF5CF3, in the UV–VUV region by electron energy loss spectroscopy

Electron energy loss spectroscopy (EELS) has been used to study the photo-absorption spectrum of trifluoromethyl sulphur pentafluoride (SF₅CF₃) for the first time. Comparison is made with the EELS spectrum of sulphur hexafluoride (SF₆). The photolysis of the compound is discussed with relevance to estimated lifetimes in the atmosphere. It is estimated that the lifetime of SF₅CF₃ is of the order of 1000 years.     

脉冲HF化学激光体系中的放电模式分析

采用面阵滑闪火花预电离诱导的平行板放电结构,研究了SF6-C2H6混合气体中的脉冲放电模式,确认了不同放电条件下存在自持体放电(SSVD)和电弧放电两种模式,且两种模式可以互相转化。SSVD模式放电电流波形主要由电容电压和气压决定,气体混合比和储能电容值对其影响很小。SSVD电流峰值随电容电压增加基本线性增加,随气压增加线性减小,分析表明这一特性是因为SSVD是由多个同步电子雪崩在时空上叠加而成,属于a过程主导的电子雪崩放电。     

Vibrational energy transfer between molecules dissolved in cryogenic liquids

Results from recent papers on vibrational energy transfer in cryogenic liquids are discussed. An overview of the significance of these results is given especially with respect to failures of the Isolated Binary Collision hypothesis for both near-resonant and non-resonant energy transfer. Preliminary results obtained for energy exchange between CO isotopes are reported and a new explanation is suggested for the solvation effects of liquid N₂/Ar mixtures on the non-resonant deactivation of N₂(v=1).     

Modeling the propagation of long, intense microwave pulses inmixtures of air and SF6

Self-consistent equations-Maxwell's equations and the electron fluid transport equations-are used to study the interaction of long, intense microwave pulses with gases. The threshold for breakdown is a factor of seven higher in SF₆ than in air. This difference is attributed to the fact that SF₆ is an insulator. When SF₆ was mixed with air, the breakdown threshold increased with the increase in the percentage of SF₆. Introducing 5-10% of SF₆ in air increased the breakdown threshold by a factor of 3-4. The electron density and conductivity and the plasma frequency increased as the pulse intensity increased. The growth rates of the electron density and conductivity were much higher in air than in SF₆     

Surface photoacoustic spectroscopy - a new technique for the study of surface vibrations

Photoacoustic studies of SF₆ adsorbed on Ag surfaces have been performed with a CO₂ laser. Simultaneous XPS measurements clearly demonstrate submonolayer surface sensitivity of photoacoustic spectroscopy under UHV conditions. The photoacoustic spectrum at 0.2 monolayer surface coverage shows a characteristic SF₆ vibrational band. Furthermore, XPS spectra exhibit fine structures indicating distinctive SF₆-Ag interactions.     

Single boron atom anchored on graphitic carbon nitride nanosheet (B/g-C2N) as a photocatalyst for nitrogen fixation: A first-principles study

It is essential to explore high efficient catalysts for nitrogen reduction in ammonia production. Based on the first-principles calculation, we find that B/g-C₂N can serve as high performance photocatalyst in N₂ fixation, where single boron atom is anchored on the g-C₂N to form B/g-C₂N. With the introduction of B atom to g-C₂N, the energy gap reduces from 2.45 eV to 1.21 eV and shows strong absorption in the visible light region. In addition, N₂ can be efficiently reduced on B/g-C₂N through the enzymatic mechanism with low onset potential of 0.07 V and rate-determining barrier of 0.50 eV. The "acceptance-donation" interaction between B/g-C₂N and N₂ plays a key role to active N₂, and the BN₂ moiety of B/g-C₂N acts as active and transportation center. The activity originates from the strong interaction between 1π1π^* orbitals of N₂ and molecular orbitals of B/g-C₂N, the ionization of 1π orbital and the filling of 1π^* orbital can increase the N≡N bond length greatly, making the activation of N₂. Overall, this work demonstrates that B/g-C₂N is a promising photocatalyst for N₂ fixation.